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    Understanding the Broadband Gateway Exception Handling

    The MobileNext Broadband Gateway processes GPRS tunneling protocol (GTP) and IP packets as they make their way from an input interface to an output interface, upstream from mobile device to IP network or downstream from IP network to mobile device. Usually, the packet processing is handled at the hardware level. However, certain exception packets follow a path through software.

    Figure 1: GTP-C Handling

    GTP-C Handling

    As shown in Figure 1, control plane packets such as session creation requests arriving on a Gn or S5 (or S8) interface are sent to an anchor session Dense Port Concentrator (DPC) for processing. The session DPC load-balances and selects anchor interface DPCs or Modular Port Concentrators (MPCs) (housing the Packet Forwarding Engines) for the user session, and all subsequent data packets for that session flow through the anchor Packet Forwarding Engine. Mid-session control packets, such as those changing session parameters due to mobility, are still sent to the anchor session DPC and associated PICs. In general, upstream and downstream data flows are handled directly by the anchor Packet Forwarding Engine.

    There are four exceptions to the general rule that user packets flow only through Packet Forwarding Engine hardware:

    • Anchor Packet Forwarding Engine failovers (N:1)
    • Reassembly of GTP-U and mobility control plane (for instance, authentication, authorization, and accounting [AAA]) fragments
    • IPv6 router advertisements and router solicitation packet handling
    • GTP-U error indication generation

    Only IP fragment reassembly and IPv6 router advertisements have parameters you can configure on the broadband gateway. (Anchor Packet Forwarding Engine configuration is part of the basic chassis configuration and aggregated Packet Forwarding Engines for failover are part of redundancy configuration).

    Published: 2011-11-16